The effect of water stress on leaf sugars and photosynthesis was examined in clones of Acacia auriculiformis in Darwin, northern Australia. Compared with the wet season or irrigated or watered-site plants, phyllodes of plants grown in the dry season on unirrigated or water-stressed sites had significantly higher contents of pinitol and total sugars. The pinitol content constituted 50% of the phyllode total sugars content compared with 17% for fructose, 20% for glucose, and <10% for sucrose. Field-grown A. auriculiformis accumulated more pinitol but less sucrose than seedlings grown in the shade-house. Under water-stress conditions, phyllode total sugars decreased 15% in seedlings but increased 30% in trees in the field. These differences probably reflect the different developmental stages and different light levels between seedlings and trees. Thus, the contents of different sugars may be involved in osmotic adjustment during water stress in A. auriculiformis.